In order to effectively and efficiently control periodontal diseases on an individual and a public health level, a better understanding of the specific etiology and pathogenesis of the disorders must be obtained. This proposal represents the effort of scientists experienced in oral microbiology, immunology, clinical periodontology and electron microscopy to learn more about the importance of Actinobacillus actin omycetemcomitans, Bacteroides gingivalis and Bacteroides intermedius in adult periodontitis. These organisms have been implicated in destructuve period periodontitis. However, most microbiological studies are difficult to interpret because they are cross-sectional in nature and they do not distinguish between actively progressing and healing periodontal sites. This proposal includes a longitudinal study of adult periodontitis patients aiming at (1) determining whether periodontitis patients with one or more of the 3 test bacteria demonstrate an increased incidence of periodontal breakdown than individuals with few or none of these bacteria, (2) elucidating whether systemic and local antibodies to these bacteria are diagnostic of periodontal infection and may modulate periodontal disease activity, and (3) ascertaining if bacterial invasion of the periodontal connective tissue is related to periodontal disease activity. Treated periodontitis patients (sites) with one or more of the 3 test bacteria and bacterial negative patients (sites) will be followed clinically, microbiologically and immunologically over a period of 4 1/2 years. The periodontal disease activity will be determined by changes in probing periodontal attachment level. The subgingival microflora will be determined by nonselective and selective culturing and indirect immunofluorescence. Serum, saliva and gingival crevice fluid antibodies against various bacterial antigen preparations will be assessed by ELISA. Bacterial invasion will be evaluated by light and electron microscopy using indirect immunofluorescence and colloidal-gold labeling to identify specific bacteria. Data will be analyzed by methods suitable for tested data in a repeated measures design. These studies have the potential to provide a clearer understanding of how selected host-parasite interactions can modulate the severity and course of destructive periodontitis in adults. The findings may lead to the formulation of new and more effective means of diagnosis, prevention and treatment of human periodontitis.